There are a few well known ‘hard problems’.

1) The unnecessary senescence of cells
2) A battery with the energy density of gasoline.
3) The constitution of dark matter (the missing ‘charges’)
4) General Artificial Intelligence.

I suspect that we will solve them in reverse order.
All of the problems are seemingly solvable – just very expensive.

https://www.quora.com/If-you-were-given-10-trillion-dollars-a-team-of-the-worlds-best-scientists-and-the-use-of-any-scientific-facility-or-facilities-in-the-world-and-you-were-told-to-solve-one-scientific-problem-what-would-it-be

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